Solid electrolytic capacitor

ABSTRACT

A solid electrolytic capacitor comprises a capacitor element including a valve-acting metal substrate including a core part and a porous part disposed on at least one principal surface of the core part, a dielectric layer formed on a surface of the porous part and a solid electrolyte layer is disposed on the dielectric layer. The capacitor element further includes a conductive layer disposed on the solid electrolyte layer. A sealing resin is located on the conductive layer and seals a principal surface of the capacitor element. A cathodic outer electrode is located on the sealing resin and is electrically connected to the conductive layer by a cathodic via electrode which extends through the sealing resin. An anodic outer electrode is electrically connected to the core part.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of International applicationNo. PCT/JP2017/030331, filed Aug. 24, 2017, which claims priority toJapanese Patent Application No. 2016-197928, filed Oct. 6, 2016, theentire contents of each of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a solid electrolytic capacitor.

BACKGROUND OF THE INVENTION

Solid electrolytic capacitors typically include a capacitor element thatincludes a valve-acting metal substrate including a core part composedof a valve metal, such as aluminum, and a porous part formed in thesurface of the core part, a dielectric layer formed in the surface ofthe porous part, a solid electrolyte layer disposed on the dielectriclayer, and a conductive layer disposed on the solid electrolyte layer.

Japanese Unexamined Patent Application Publication No. 2008-135427(“Patent Document 1” 0) discloses a solid electrolytic capacitor where aplurality of capacitor elements are stacked on top of one another. Thecapacitor elements are then electrically connected to a lead frame, andresin sealing is subsequently performed by transfer molding or the like.In another case, the capacitor elements are electrically connected to amount board, such as a printed circuit board, instead of a lead frameand resin sealing is subsequently performed.

The part of a solid electrolytic capacitor which is responsible for theformation of electrostatic capacity (hereinafter, such a part isreferred to as “capacitance formation part”) is the porous part, such asan etched layer, in which the dielectric layer is formed. It isadvantageous to reduce the distance between the capacitance formationpart and an outer electrode from which current is drawn, such as a leadframe, for reducing the ESR (equivalent series resistance) and ESL(equivalent series inductance) of a solid electrolytic capacitor.However, in the production methods used in the related art in which aplurality of capacitor elements are stacked on top of one another, thedistance between the capacitance formation part and the outer electrodeis large and, accordingly, the ESR and ESL of a solid electrolyticcapacitor are reduced disadvantageously. Furthermore, in the productionmethods used in the related art, it is difficult to increase the ratioof the volume of the capacitance formation part to the overall volume ofthe capacitor. Thus, it is difficult to produce a thin solidelectrolytic capacitor having a low ESR and a low ESL by the productionmethods used in the related art.

The present invention was made in order to address the above issues. Anobject of the present invention is to provide a solid electrolyticcapacitor that may have a low ESR, and a low ESL, and a small thickness.

BRIEF SUMMARY OF THE INVENTION

The solid electrolytic capacitor according to the present inventionincludes a capacitor element including a valve-acting metal substrateincluding a core part and a porous part disposed on at least oneprincipal surface of the core part, a dielectric layer formed in asurface of the porous part, a solid electrolyte layer disposed on thedielectric layer, and a conductive layer disposed on the solidelectrolyte layer; a sealing resin with which a principal surface of thecapacitor element is sealed; a cathodic outer electrode electricallyconnected to the conductive layer; and an anodic outer electrodeelectrically connected to the core part. The sealing resin and thecathodic outer electrode are disposed on and above the conductive layerin this order. The sealing resin disposed on the conductive layer isprovided with a cathodic via electrode formed in the sealing resin, thecathodic via electrode penetrating the sealing resin. The conductivelayer is electrically drawn to a surface of the sealing resin throughthe cathodic via electrode. The cathodic via electrode exposed at thesurface of the sealing resin is connected to the cathodic outerelectrode.

In the solid electrolytic capacitor according to the present invention,the cathodic via electrode may be a paste electrode including a materialformed by curing a conductive paste, and the cathodic via electrode maybe a columnar metal pin.

In the solid electrolytic capacitor according to the present invention,when viewed in the direction of the normal to the principal surface ofthe capacitor element, the cathodic outer electrode preferably has alarger size than the cathodic via electrode so as to cover the cathodicvia electrode.

In a first embodiment of the present invention, an insulating layer isinterposed between the core part and the sealing resin; the insulatinglayer, the sealing resin, and the anodic outer electrode are disposed onand above the core part in this order; a first anodic via electrode isformed in the sealing resin disposed on the insulating layer so as topenetrate the sealing resin, and a second anodic via electrode is formedin the insulating layer disposed on the core part so as to penetrate theinsulating layer; the core part is electrically drawn to the surface ofthe sealing resin through the first and second anodic via electrodes;and the first anodic via electrode exposed at the surface of the sealingresin is connected to the anodic outer electrode.

In the first embodiment of the present invention, on a principal surfaceof the valve-acting metal substrate, a surface of the core part ispreferably at a lower level than the surface of the porous part.

In the first embodiment of the present invention, the first and secondanodic via electrodes may be plated electrodes, and the first and secondanodic via electrodes may be paste electrodes including a materialformed by curing a conductive paste.

In the first embodiment of the present invention, each of the first andsecond anodic via electrodes preferably has a reversely taperedcross-sectional shape, the width of the reversely taperedcross-sectional shape increasing in the direction from the core parttoward the anodic outer electrode.

In the first embodiment of the present invention, the first and secondanodic via electrodes may be columnar metal pins.

In the first embodiment of the present invention, the insulating layermay be composed of the same material as the sealing resin.

In a second embodiment of the present invention, the sealing resin andthe anodic outer electrode are disposed on and above the core part inthis order; a first anodic via electrode is formed in the sealing resindisposed on the core part so as to penetrate the sealing resin; thefirst anodic via electrode is arranged to come into direct contact withthe core part; the core part is electrically drawn to the surface of thesealing resin through the first anodic via electrode; and the firstanodic via electrode exposed at the surface of the sealing resin isconnected to the anodic outer electrode.

In the second embodiment of the present invention, on a principalsurface of the valve-acting metal substrate, a surface of the core partis preferably at a higher level than the surface of the porous part orat the same level as the surface of the porous part.

In the second embodiment of the present invention, the first anodic viaelectrode may be a plated electrode, and the first anodic via electrodemay be a paste electrode including a material formed by curing aconductive paste.

In the second embodiment of the present invention, the first anodic viaelectrode preferably has a reversely tapered cross-sectional shape, thewidth of the reversely tapered cross-sectional shape increasing in thedirection from the core part toward the anodic outer electrode.

In the second embodiment of the present invention, the first anodic viaelectrode may be a columnar metal pin.

In the first and second embodiments of the present invention, whenviewed in the direction of the normal to the principal surface of thecapacitor element, the anodic outer electrode preferably has a largersize than the first anodic via electrode so as to cover the first anodicvia electrode.

In the solid electrolytic capacitor according to the present invention,the anodic outer electrode and the cathodic outer electrode may be metalelectrodes including a metal film; the anodic outer electrode and thecathodic outer electrode may be paste electrodes including a materialformed by curing a conductive paste; the anodic outer electrode may be aball-like terminal; and the cathodic outer electrode may be a ball-liketerminal.

In the solid electrolytic capacitor according to the present invention,a surface of the solid electrolytic capacitor, the surface being otherthan a surface that includes the anodic outer electrode and the cathodicouter electrode, may be covered with another insulating layer.

In the solid electrolytic capacitor according to the present invention,a stress relaxation layer may be interposed between the capacitorelement and the sealing resin; and a damp-proof membrane may beinterposed between the capacitor element and the sealing resin.

According to the present invention, a solid electrolytic capacitor thatmay have a low ESR, and a low ESL, and a small thickness can beprovided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1(a) is a schematic cross-sectional view of an example of a solidelectrolytic capacitor according to a first embodiment of the presentinvention.

FIG. 1(b) is a schematic cross-sectional view of an example of acapacitor element included in the solid electrolytic capacitorillustrated in FIG. 1(a).

FIG. 1(c) is a schematic perspective view of an example of a capacitorelement included in the solid electrolytic capacitor illustrated in FIG.1(a).

FIGS. 2-1(a) through 2-2(l) are schematic perspective views illustratingan example of the method for producing the solid electrolytic capacitor1 illustrated in FIG. 1(a).

FIG. 3(a) is a schematic cross-sectional view of an example of a solidelectrolytic capacitor according to a second embodiment of the presentinvention

FIG. 3(b) is a schematic cross-sectional view of an example of acapacitor element included in the solid electrolytic capacitorillustrated in FIG. 3(a)

FIG. 3(c) is a schematic perspective view of an example of a capacitorelement included in the solid electrolytic capacitor illustrated in FIG.3(a).

FIGS. 4-1(a) through 4-2(k) are schematic perspective views illustratingan example of the method for producing the solid electrolytic capacitor2 illustrated in FIG. 3(a).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings wherein like numerals indicate likeelements, several preferred embodiments of the invention will bedescribed. However, the present invention is not limited to thestructures described below. Variations and modifications may be madewithout departing from the spirit and scope of the present invention.The present invention also includes a combination of two or more of thedesirable structures of the present invention which are described below.

It should be understood that the following embodiments are merelyillustrative and partial replacements or combinations of structuresdescribed in different embodiments are also possible. In the secondembodiment and thereafter, the description of items common to the firstembodiment is omitted, and only the differences are described.Especially, similar actions and effects of a similar structure is notmentioned in each of the embodiments.

In the solid electrolytic capacitor according to certain embodiments ofthe present invention, the sealing resin and the cathodic outerelectrode are disposed on the conductive layer in this order, thecathodic via electrode is formed in the sealing resin disposed on theconductive layer, and the conductive layer is electrically drawn to thesurface of the sealing resin through the cathodic via electrode. Sincethe functions are concentrated on only one side of the valve-actingmetal substrate and the sizes of the functional layers other than thecapacitance formation part (the part responsible for the formation ofelectrostatic capacity) are minimized, the ratio of the volume of thecapacitance formation part to the overall volume of the capacitor may beincreased. This enables an increase in the volumetric efficiency of thecapacitance formation part and the production of a thin solidelectrolytic capacitor.

Specifically, arranging the outer electrodes on the surface of thesealing resin eliminates the need to use a thick electrode, such as amount board or a lead frame. This enables the overall thickness of theproduct to be reduced while maintaining the thicknesses of thefunctional layers inside the capacitor element.

In addition, the distance the conductive layer disposed in a cathodepart is drawn to the outer electrode is small at any position. Thisenables the ESR and ESL of a solid electrolytic capacitor to be reducedcompared with solid electrolytic capacitors known in the related art.

First Embodiment

In the first embodiment of the present invention, an insulating layer isinterposed between the core part and the sealing resin; the insulatinglayer, the sealing resin, and the anodic outer electrode are disposed onand above the core part in this order; a first anodic via electrode isformed in the sealing resin disposed on the insulating layer, and asecond anodic via electrode is formed in the insulating layer disposedon the core part; and the core part is electrically drawn to the surfaceof the sealing resin through the first and second anodic via electrodes.One of the structural advantages of the first embodiment of the presentinvention is that the insulating layer, which comes into direct contactwith the porous part, and the sealing resin may be composed of differentmaterials. Since the surface of the cathode part which faces theprincipal surface of the capacitor element is covered with the sealingresin and the cathodic outer electrode and therefore has a substantiallyhermetically sealed structure, the possible routes through whichmoisture may enter from the outside are primarily the insulating layerand the interfaces between the above layers. Forming the insulatinglayer using a material having high adhesion and high vapor resistanceenables the production of a solid electrolytic capacitor havingexcellent reliability. Furthermore, the anode and cathodic outerelectrodes may be disposed on the same side. This makes it possible toproduce a thin solid electrolytic capacitor.

As illustrated in FIGS. 1(a) and 1(b), the solid electrolytic capacitor1 of the first preferred embodiment includes a capacitor element 10, asealing resin 20, a cathodic outer electrode 30, and an anodic outerelectrode 40. The capacitor element 10 includes a valve-acting metalsubstrate 11 which includes a core part 11 b and a porous part 11 adisposed on a principal surface of the core part 11 b, a dielectriclayer 12 formed on the surface of the porous part 11 a, a solidelectrolyte layer 13 disposed on the dielectric layer 12, and aconductive layer 14 disposed on the solid electrolyte layer 13. Aninsulating layer 15 is disposed on the outer periphery of the core part11 b and insulates the sealing resin 20 from the core part 11 b and thelateral edges of the porous part 11 a as illustrated in FIG. 1(a).

In the solid electrolytic capacitor 1 illustrated in FIG. 1(a), the topsurface of the valve acting metal substrate 11 includes the top surfaceof the porous part 11 a and the top surface of the core part 11 blocated laterally outward of the porous part (i.e., left and right ofthe porous part 11 a as viewed in FIGS. 1(a) and 1(b). In thisembodiment, the top surface of the core part 11 b is located below thetop surface of the porous part 11 a. Alternatively, the top surface ofthe core part 11 a can be above or at the same level as the top surfaceof the porous part 11 a. The foregoing references to “top surface” iswith reference to the orientation of the core part 11 b and the porouspart 11 a as viewed in FIGS. 1(a) and 1(b).

It is preferable that the porous part 11 a be disposed at the center ofthe valve-acting metal substrate 11 and the core part 11 b be disposedboth at the center and on the peripheral portion of the valve-actingmetal substrate 11 as illustrated in FIGS. 1(b) and 1(c).

In this embodiment, the upper principal surface of the capacitor element10 is sealed with the sealing resin 20 such that the sealing resin 20 isdisposed on the conductive layer 14 and the insulating layer 15 andcovers the entire upper principal surface of the capacitor element 10.

The cathodic outer electrode 30 is electrically connected to theconductive layer 14. In the solid electrolytic capacitor 1 illustratedin FIG. 1(a), the sealing resin 20 and the cathodic outer electrode 30are disposed on and above the conductive layer 14 in this order, andcathodic via electrodes 31 are formed in the sealing resin 20 disposedon the conductive layer 14 so as to penetrate the sealing resin 20. Theconductive layer 14 (a cathode part 21) is electrically drawn to thesurface of the sealing resin 20 by the cathodic via electrodes 31. Theportion of the cathodic via electrodes 31 exposed at the surface of thesealing resin 20 are connected to the cathodic outer electrode 30.

The form of the cathodic via electrodes 31 is not limited; the cathodicvia electrodes 31 may be, for example, paste electrodes. The term “pasteelectrode” used herein refers to an electrode composed of a materialformed by curing a conductive paste. Cathodic via electrodes 31 that arepaste electrodes may be readily formed by forming bump electrodes,covering the bump electrodes with the sealing resin, and trimming thesealing resin as described below.

In the example illustrated in FIG. 1(a), the cathodic via electrodes 31have a tapered cross-sectional shape the width of which increases in thedirection from the cathodic outer electrode 30 toward the conductivelayer 14. In the case where the cathodic via electrodes 31 are pasteelectrodes, the cathodic via electrodes 31 may, for example, have thetapered cross-sectional shape or a rectangular cross-sectional shape thewidth of which substantially does not change in the direction from thecathodic outer electrode 30 toward the conductive layer 14.

The cathodic via electrodes 31 may be columnar metal pins. In the casewhere the cathodic via electrodes 31 are the metal pins, the cathodicvia electrodes 31 preferably have a rectangular cross-sectional shapethe width of which substantially does not change in the direction fromthe cathodic outer electrode 30 toward the conductive layer 14. Examplesof the shape of the metal pins include a cylindrical shape.

Although four cathodic via electrodes 31 are illustrated in FIG. 1(a),more or less cathodic via electrodes 31 may be used. The number of thecathodic via electrodes 31 is at least one.

The height of the cathodic via electrodes 31 is preferably equal to thethickness of the sealing resin 20. The height of the cathodic viaelectrodes 31 is not limited and preferably 5 μm or more and 200 μm orless.

The form of the cathodic outer electrode 30 is not limited; the cathodicouter electrode 30 may be, for example, a metal electrode or a pasteelectrode. The term “metal electrode” used herein refers to an electrodecomposed of a metal film. Examples of the metal film include a platingfilm, a sputtered film, and a vapor-deposited film.

In the case where the cathodic outer electrode 30 is a metal electrode,the anodic outer electrode 40 is preferably also a metal electrode andmay be a paste electrode. Similarly, in the case where the cathodicouter electrode 30 is a paste electrode, the anodic outer electrode 40is preferably also a paste electrode and may be a metal electrode. Inthe case where a metal electrode is used, the outer electrode ispreferably grown directly on the surface of the metal constituting thevia electrode. This may reduce the electric resistance. In the casewhere a paste electrode is used, the adhesion of the outer electrode tothe via electrode is increased. This may enhance the reliability.

The shape of the cathodic outer electrode 30 is also not limited. Whenviewed in the direction of the normal to a principal surface of thecapacitor element 10, the cathodic outer electrode 30 preferably has alarger size than the cathodic via electrodes 31 so as to cover thecathodic via electrodes 31.

The cathodic outer electrode 30 may be a ball-like terminal disposed onthe cathodic via electrodes 31. Examples of the ball-like terminalinclude a BGA (ball grid array) terminal.

The anodic outer electrode 40 is preferably electrically connected tothe core part 11 b. In the solid electrolytic capacitor 1 illustrated inFIG. 1(a), the insulating layer 15, the sealing resin 20, and the anodicouter electrode 40 are disposed on and above the core part 11 b in thisorder. A first anodic via electrode 41 is preferably formed in thesealing resin 20 disposed on the insulating layer 15 so as to penetratethe sealing resin 20. A second anodic via electrode 42 is preferablyformed in the insulating layer 15 disposed on the core part 11 b so asto penetrate the insulating layer 15. The core part 11 b (an anode part22) is electrically drawn to the surface of the sealing resin 20 throughthe first and second anodic via electrodes 41 and 42. The first anodicvia electrode 41 exposed at the surface of the sealing resin 20 isconnected to the anodic outer electrode 40. Although FIG. 1(a)illustrates a boundary line between the first and second anodic viaelectrodes 41 and 42 in order to distinguish the first and second anodicvia electrodes 41 and 42 from each other, the first and second anodicvia electrodes may be formed in one continuous piece.

The form of the first anodic via electrode 41 is not limited; the firstanodic via electrode 41 may be, for example, a plated electrode or apaste electrode. The form of the second anodic via electrode 42 is alsonot limited; the second anodic via electrode 42 may be, for example, aplated electrode or a paste electrode. In the case where the firstanodic via electrode 41 is a plated electrode, the second anodic viaelectrode 42 is preferably also a plated electrode and may be a pasteelectrode. Similarly, in the case where the first anodic via electrode41 is a paste electrode, the second anodic via electrode 42 ispreferably also a paste electrode and may be a plated electrode.

In the example illustrated in FIG. 1(a), the first and second anodic viaelectrodes 41 and 42 each have a reversely tapered cross-sectionalshape, i.e., one where the width of the via electrode increases in thedirection from the core part 11 b toward the anodic outer electrode 40.In the case where the first and second anodic via electrodes 41 and 42are plated electrodes, the first and second anodic via electrodes 41 and42 preferably have the reversely tapered cross-sectional shape. In sucha case, it becomes possible to increase the size of the capacitanceformation part while maintaining the area of the region that can besealed with the resin. Furthermore, when the first and second anodic viaelectrodes 41 and 42 have the reversely tapered cross-sectional shape, ahigh fill-up efficiency may be achieved during plating.

The first and second anodic via electrodes 41 and 42 may be columnarmetal pins. In the case where the first and second anodic via electrodes41 and 42 are metal pins, the first and second anodic via electrodes 41and 42 preferably have a rectangular cross-sectional shape the width ofwhich substantially does not change in the direction from the anodicouter electrode 40 toward the core part 11 b. Examples of the shape ofthe metal pins include a cylindrical shape.

Although a single first anodic via electrode 41 and a single secondanodic via electrode 42 are illustrated in FIG. 1(a), more viaelectrodes 41 and 42 may be used. Although the anode part 22 is presenton the left and right sides of the solid electrolytic capacitor 1illustrated in FIG. 1(a) and the first and second anodic via electrodes41 and 42 are formed in the right anode part 22, the first and secondanodic via electrodes 41 and 42 may be also formed in the left anodepart 22.

The form of the anodic outer electrode 40 is not limited; the anodicouter electrode 40 may be, for example, a metal electrode or a pasteelectrode.

The shape of the anodic outer electrode 40 is not limited. When viewedin the direction of the normal to a principal surface of the capacitorelement 10, the anodic outer electrode 40 preferably has a larger sizethan the first anodic via electrode 41 so as to cover the first anodicvia electrode 41.

The anodic outer electrode 40 may be a ball-like terminal disposed onthe first anodic via electrode 41. Examples of the ball-like terminalinclude a BGA (ball grid array) terminal.

In FIG. 1(a), the cathodic outer electrode 30 and the anodic outerelectrode 40 are arranged so that they do not come into contact witheach other and are insulated from each other on the surface of thesealing resin 20.

Various modifications are possible. For example, a surface of the solidelectrolytic capacitor 1 other than the surface that includes the anodicouter electrode 40 and the cathodic outer electrode 30 may optionally becovered with another insulating layer in order to protect the othersurface. By way of another example, example, a stress relaxation layerand a damp-proof membrane may optionally be interposed between thecapacitor element and the sealing resin in order to protect thecapacitor element.

The valve-acting metal substrate included in the solid electrolyticcapacitor according to the present invention is composed of avalve-action metal that has a “valve action”. Examples of thevalve-action metal include metal elements such as aluminum, tantalum,niobium, titanium, and zirconium and alloys including the above metalelements. Among the above valve-action metals, aluminum and an aluminumalloy are preferable.

The valve-acting metal substrate is preferably plate-like in shape andis more preferably foil-like. The porous part and the core part aredisposed on at least one principal surface of the valve-acting metalsubstrate. Alternatively, the porous part and the core part may bedisposed on each of the principal (typically opposed) surfaces of thevalve-acting metal substrate. The porous part is preferably an etchedlayer formed in the surface of the core part.

The thickness of the core part is preferably 5 μm or more and 100 μm orless. The thickness of the porous part (the thickness of one porous partexcept the core part) is preferably 5 μm or more and 200 μm or less.

In the solid electrolytic capacitor according to the present invention,the dielectric layer is formed in the surface of the porous part of thevalve-acting metal substrate. Reflecting the conditions of the surfaceof the porous part, the dielectric layer disposed in the surface of theporous part is porous and has a surface with fine irregularities. Thedielectric layer is preferably a film composed of an oxide of thevalve-action metal. In the case where, for example, an aluminum foil isused as a valve-acting metal substrate, a dielectric layer that is anoxide film may be formed by subjecting the surface of the aluminum foilto an anodic oxidation treatment (i.e., chemical conversion) in anaqueous solution containing ammonium adipate or the like. It ispreferable that the dielectric layer be not formed on the surface of thecore part.

Examples of the material constituting the insulating layer included inthe solid electrolytic capacitor according to the present inventioninclude insulative resins, such as a polyphenylsulfone resin, apolyethersulfone resin, a cyanate ester resin, a fluororesin (e.g.,tetrafluoroethylene or a tetrafluoroethylene-perfluoroalkyl vinyl ethercopolymer), a polyimide resin, and a polyamide imide resin andderivatives and precursors of the above insulative resins. Theinsulating layer may be composed of the same material as the sealingresin described below.

Examples of the material constituting the solid electrolyte layerincluded in the solid electrolytic capacitor according to the presentinvention include conductive high-molecular compounds, such aspolypyrroles, polythiophenes, and polyanilines. Among the abovecompounds, polythiophenes are preferable andpoly(3,4-ethylenedioxythiophene), that is, “PEDOT”, is particularlypreferable. The above conductive high-molecular compounds may include adopant, such as polystyrene sulfonic acid (PSS). The solid electrolytelayer preferably includes an inner layer that fills the pores (recesses)of the dielectric layer and an outer layer that covers the dielectriclayer.

The conductive layer included in the solid electrolytic capacitoraccording to the present invention preferably includes a carbon layerthat serves as a backing and a silver layer disposed on the carbonlayer. The conductive layer may include only a carbon layer or a silverlayer. The conductive layers, such as a carbon layer and a silver layer,are preferably arranged to cover the entire surface of the solidelectrolyte layer.

Examples of the material constituting the sealing resin included in thesolid electrolytic capacitor according to the present invention includean epoxy resin and a phenol resin.

The solid electrolytic capacitor 1 illustrated in FIG. 1(a) ispreferably produced by the following method.

FIGS. 2(a) through 2-2(l) are schematic perspective views illustratingan example of the method for producing the solid electrolytic capacitor1 illustrated in FIG. 1(a).

A valve-acting metal substrate 11 that includes a core part 11 b and aporous part 11 a, such as an etched layer, disposed on the entirety of aprincipal surface of the core part 11 b is prepared (or obtained) asillustrated in FIG. 21(a). A dielectric layer 12 is formed in thesurface of the porous part 11 a as illustrated in FIG. 2-1(b). Asdescribed above, in the case where, for example, an aluminum foil isused as a valve-acting metal substrate, a dielectric layer that is anoxide film may be formed by subjecting the surface of the aluminum foilto an anodic oxidation treatment (i.e., chemical conversion) in anaqueous solution containing ammonium adipate or the like.

A portion of the dielectric layer 12 and a portion of the porous part 11a are removed with a laser or the like such that the core part 11 b,which serves as an anode part, is exposed as illustrated in FIG. 2-1(c).In this case, the surface of the core part 11 b is at a lower level thanthe surface of the porous part 11 a (as viewed in FIG. 2(c)). In FIG.2-1(c), a portion of the core part 11 b which acts as the peripheralportion of the valve-acting metal substrate 11 is exposed.Alternatively, the dielectric layer 12 may be formed after the core part11 b has been exposed by removing a portion of the porous part 11 a. Insuch a case, it is preferable to form a mask on the surface of the corepart 11 b in order to prevent the dielectric layer 12 from being formedin the surface of the core part 11 b.

In another case, in order to increase the production efficiency, a foilthat has been subjected to chemical conversion, that is, a chemicallyconverted foil, may be used as a valve-acting metal substrate providedwith a dielectric layer formed in the surface of the metal base. In sucha case, since the dielectric layer is disposed on the entirety of thechemically converted foil, the core part, which serves as an anode part,may be exposed by removing a portion of the dielectric layer and aportion of the porous part with a laser or the like.

An insulating layer 15 is formed on the core part 11 b by applying aninsulative resin to the core part 11 b as illustrated in FIG. 2-1(d).The method for applying the insulative resin is not limited. Forexample, a method in which a dispenser is used and screen printing maybe used.

A solid electrolyte layer 13 is formed on the dielectric layer 12 asillustrated in FIG. 2-1(e). The solid electrolyte layer may be formedby, for example, forming a polymer film composed ofpoly(3,4-ethylenedioxythiophene) or the like on the surface of thedielectric layer using a coating liquid containing a monomer such as3,4-ethylenedioxythiophene or by applying a dispersion containing apolymer such as poly(3,4-ethylenedioxythiophene) onto the surface of thedielectric layer and drying the resulting coating film. It is preferableto form the solid electrolyte layer by forming an inner layer that fillsthe pores (recesses) of the dielectric layer and subsequently forming anouter layer that covers the dielectric layer.

A conductive layer 14 is formed on the solid electrolyte layer 13 asillustrated in FIG. 2-1(f). It is preferable to form the conductivelayer by forming a carbon layer and a silver layer successively.Alternatively, only a carbon layer may be formed. In another case, onlya silver layer may be formed. The carbon layer and the silver layer maybe formed by, for example, applying a carbon paste drying the resultingcoating film, subsequently applying the silver paste, and drying theresulting coating film.

Bump electrodes (paste electrodes) 31′ are formed on the conductivelayer 14 using a conductive paste as illustrated in FIG. 2-2(g).Subsequently, a sealing resin 20 is disposed on the conductive layer 14and the insulating layer 15 as illustrated in FIG. 2-2(h) in order toperform sealing with the sealing resin 20 such that the bump electrodes31′ are completely covered with the sealing resin 20. The sealing resinmay be formed by resin molding or the like. Subsequently, the sealingresin 20 is trimmed such that the surfaces of the bump electrodes 31′are exposed as illustrated in FIG. 2-2(i). Thus, cathodic via electrodes31 are formed in the sealing resin 20 disposed on the conductive layer14 so as to penetrate the sealing resin 20. Note that, the cathodic viaelectrodes 31 are substantially the same as the bump electrodes 31′.

Via holes 45 are formed in the insulating layer 15 and the sealing resin20 that are disposed on and above the core part 11 b with a laser or thelike so as to penetrate the insulating layer 15 and the sealing resin 20as illustrated in FIG. 2-2(j). Subsequently, as illustrated in FIG.2-2(k), first anodic via electrodes 41 are formed in the sealing resin20 disposed on the insulating layer 15 so as to penetrate the sealingresin 20, and second anodic via electrodes 42 (not illustrated) areformed in the insulating layer 15 disposed on the core part 11 b so asto penetrate the insulating layer 15. The first anodic via electrodesmay be, for example, plated electrodes or paste electrodes. The secondanodic via electrodes may be, for example, plated electrodes or pasteelectrodes.

A cathodic outer electrode 30 electrically connected to the conductivelayer 14 through the cathodic via electrodes 31 and an anodic outerelectrode 40 electrically connected to the core part 11 b through thesecond anodic via electrodes 42 and the first anodic via electrodes 41are formed as illustrated in FIG. 2-2(l). The anodic outer electrode maybe, for example, a metal electrode, a paste electrode, or a ball-liketerminal. The cathodic outer electrode may be, for example, a metalelectrode, a paste electrode, or a ball-like terminal.

The solid electrolytic capacitor 1 illustrated in FIG. 1(a) ispreferably produced by the above-described method.

Second Embodiment

In the second embodiment of the present invention, the sealing resin andthe anodic outer electrode are disposed on and above the core part inthis order; a first anodic via electrode is formed in the sealing resindisposed on the core part; the first anodic via electrode is arranged tocome into direct contact with the core part; and the core part iselectrically drawn to the surface of the sealing resin through the firstanodic via electrode. In the structure according to the secondembodiment of the present invention, the core part is arrangedsubstantially close to the anodic outer electrode and the length of thevia electrodes having a narrow conductive path may be relatively reducedaccordingly. This makes it possible to reduce the overall resistance ofthe capacitor and pass a large current through the capacitor. Inparticular, in the case where a three-terminal capacitor is used as acircuit by-pass capacitor, the structure in which the proportion of theconductor in the conductive path is high as in the second embodiment maybe advantageous, because it is desirable to maximize thecurrent-carrying capacity between anodes. Furthermore, the anode andcathodic outer electrodes may be disposed on the same side. This makesit possible to produce a thin solid electrolytic capacitor.

The solid electrolytic capacitor 2 illustrated in FIG. 3(a) includes acapacitor element 10′, a sealing resin 20, a cathodic outer electrode30, and an anodic outer electrode 40. As illustrated in FIGS. 3(a) and3(b), the capacitor element 10′ includes a valve-acting metal substrate11 including a core part 11 b and a porous part 11 a disposed on aprincipal surface of the core part 11 b, a dielectric layer 12 formed inthe surface of the porous part 11 a, a solid electrolyte layer 13disposed on the dielectric layer 12, and a conductive layer 14 disposedon the solid electrolyte layer 13. An insulating layer 15 is disposed ona principal surface of the valve-acting metal substrate 11 and surroundsthe outer periphery of the dielectric layer 12, the solid electrolytelayer 13 and the conductive layer 14 and the as illustrated in FIG.3(a). While not shown in FIG. 3(c), the insulating layer 15 preferablyextends around the entire periphery of the insulating layer 14 as viewedin FIG. 3(c).

In the solid electrolytic capacitor 2 illustrated in FIGS. 3(a), corepart 11 b has a recess in which the porous part 11 a is located. This isshown more clearly in FIGS. 3(b) and 3(c). It is preferable that theporous part 11 a be disposed at the center of the valve-acting metalsubstrate 11 and the core part 11 b be disposed both below the core part11 b and laterally outward of (peripherally of) the core party 11 b asillustrated in FIGS. 3(b) and 3(c). It is also preferable that theinsulating layer 15 be disposed on the inner walls of the recess betweenthe porous part 11 a and the outer edges of the dielectric 12, the solidelectrolyte layer 13 and the conductive layer 14. While the foregoingstructure is preferred, the recess need not be formed in thevalve-acting metal substrate 11, and the surface of the core part 11 bmay be at the same level as the surface of the porous part 11 a or at alower level than the surface of the porous part 11 a on the principalsurface of the valve-acting metal substrate 11.

A principal surface of the capacitor element 10′ is sealed with thesealing resin 20. In the solid electrolytic capacitor 2 illustrated inFIG. 3(a), the sealing resin 20 is disposed on the conductive layer 14and the core part 11 b so as to cover the principal surface of thecapacitor element 10′.

The cathodic outer electrode 30 is electrically connected to theconductive layer 14. In the solid electrolytic capacitor 2 illustratedin FIG. 3(a), the sealing resin 20 and the cathodic outer electrode 30are disposed on and above the conductive layer 14 in this order, andcathodic via electrodes 31 are formed in the sealing resin 20 disposedon the conductive layer 14 so as to penetrate the sealing resin 20. Theconductive layer 14 (a cathode part 21) is electrically drawn to thesurface of the sealing resin 20 through the cathodic via electrodes 31.The cathodic via electrodes 31 exposed at the surface of the sealingresin 20 are connected to the cathodic outer electrode 30.

The form, cross-sectional shape, etc. of the cathodic via electrodes 31are preferably the same as in the first embodiment. The form, shape,etc. of the cathodic outer electrode 30 are also preferably the same asin the first embodiment.

The anodic outer electrode 40 is electrically connected to the core part11 b. In the solid electrolytic capacitor 2 illustrated in FIG. 3(a),the sealing resin 20 and the anodic outer electrode 40 are disposed onand above the core part 11 b in this order. A first anodic via electrode41 is formed in the sealing resin 20 disposed on the core part 11 b soas to penetrate the sealing resin 20. The first anodic via electrode 41is arranged to come into direct contact with the core part 11 b. Thecore part 11 b (an anode part 22) is electrically drawn to the surfaceof the sealing resin 20 through the first anodic via electrode 41. Thefirst anodic via electrode 41 exposed at the surface of the sealingresin 20 is connected to the anodic outer electrode 40.

The form, cross-sectional shape, etc. of the first anodic via electrode41 are preferably the same as in the first embodiment. The form, shape,etc. of the anodic outer electrode 40 are also the same as in the firstembodiment.

In FIG. 3(a), the cathodic outer electrode 30 and the anodic outerelectrode 40 are arranged not to come into contact with each other andto be insulated from each other on the surface of the sealing resin 20.

Various modification are possible. For example, a surface of the solidelectrolytic capacitor 2 which is other than the surface that includesthe anodic outer electrode 40 and the cathodic outer electrode 30 may becovered with another insulating layer in order to protect the othersurface. Moreover, a stress relaxation layer, a damp-proof membrane, andthe like may optionally be interposed between the capacitor element andthe sealing resin in order to protect the capacitor element.

The material constituting the valve-acting metal substrate included inthe capacitor element, etc. are preferably the same as in the firstembodiment. The thickness of the core part is preferably 5 μm or moreand 300 μm or less. The thickness of the porous part (the thickness ofone porous part except the core part) is preferably 5 μm or more and 200μm or less. In the case where a recess is formed in the valve-actingmetal substrate, the depth of the recess is preferably 5 μm or more and200 μm or less.

The materials constituting the dielectric layer, the solid electrolytelayer, the conductive layer, the insulating layer, and the sealing resinthat are included in the capacitor element, etc. are preferably the sameas in the first embodiment. In the case where the porous part isdisposed in the recess of the valve-acting metal substrate, it ispreferable that the solid electrolyte layer and the conductive layer benot protruded from the recess.

The solid electrolytic capacitor 2 illustrated in FIG. 3(a) ispreferably produced by the following method.

FIGS. 4-1(a) through 4-2(k) are schematic perspective views illustratingan example of the method for producing the solid electrolytic capacitor2 illustrated in FIG. 3(a).

As illustrated in FIG. 4-1(a), a recess 11′ is formed in a valve-actingmetal substrate 11 including a core part 11 b, and a porous part 11 a,such as an etched layer, is formed in the inner surface of the recess11′. The recess may be formed by any method. For example, cutting,pressing, and etching may be used. The recess 11′ and the porous part 11a may be simultaneously formed by etching. In FIG. 4-1(a), the core part11 b that surrounds the recess 11′ and acts the peripheral portion ofthe valve-acting metal substrate 11 serves as an anode part. In thiscase, the surface of the core part 11 b is at a higher level than thesurface of the porous part 11 a.

An insulating layer 15 is formed on the peripheral portion of the recess11′, which comes into contact with the core part 11 b, by applying aninsulative resin to the peripheral portion of the recess 11′ asillustrated in FIG. 4-1(b). The method for applying the insulative resinis not limited. For example, a method in which a dispenser is used andscreen printing may be used. Alternatively, the porous part 11 a may beformed in the inner surface of the recess 11′ after the insulating layer15 has been formed on the peripheral portion of the recess 11′.

A dielectric layer 12 is formed in the surface of the porous part 11 aas illustrated in FIG. 4-1(c). It is preferable to form a mask on thesurface of the core part 11 b in order to prevent the dielectric layer12 from being formed in the surface of the core part 11 b.

A solid electrolyte layer 13 is formed on the dielectric layer 12 asillustrated in FIG. 4-1(d). It is preferable to form the solidelectrolyte layer by forming an inner layer that fills the pores of thedielectric layer and subsequently forming an outer layer that covers thedielectric layer.

A conductive layer 14 is formed on the solid electrolyte layer 13 asillustrated in FIG. 4-1(e). It is preferable to form the conductivelayer by forming a carbon layer and a silver layer successively.Alternatively, only a carbon layer may be formed. In another case, onlya silver layer may be formed.

Bump electrodes (paste electrodes) 31′ are formed on the conductivelayer 14 using a conductive paste as illustrated in FIG. 4-2(f).Subsequently, a sealing resin 20 is disposed on the core part 11 b, theconductive layer 14, and the insulating layer 15 as illustrated in FIG.4-2(g) in order to perform sealing with the sealing resin 20 such thatthe bump electrodes 31′ are completely covered with the sealing resin20. The sealing resin may be formed by resin molding or the like.Subsequently, the sealing resin 20 is trimmed such that the surfaces ofthe bump electrodes 31′ are exposed as illustrated in FIG. 4-2(h). Thus,cathodic via electrodes 31 are formed in the sealing resin 20 disposedon the conductive layer 14 so as to penetrate the sealing resin 20. Thecathodic via electrodes 31 are substantially the same as the bumpelectrodes 31′.

Via holes 45 are formed in the sealing resin 20 disposed on the corepart 11 b with a laser or the like so as to penetrate the sealing resin20 as illustrated in FIG. 4-2(i). Subsequently, first anodic viaelectrodes 41 are formed in the sealing resin 20 disposed on the corepart 11 b so as to penetrate the sealing resin 20 as illustrated in FIG.4-2(j). The first anodic via electrodes may be, for example, platedelectrodes or paste electrodes.

A cathodic outer electrode 30 electrically connected to the conductivelayer 14 through the cathodic via electrodes 31 and an anodic outerelectrode 40 electrically connected to the core part 11 b through thefirst anodic via electrodes 41 are formed as illustrated in FIG. 4-2(k).The anodic outer electrode may be, for example, a metal electrode, apaste electrode, or a ball-like terminal. The cathodic outer electrodemay be, for example, a metal electrode, a paste electrode, or aball-like terminal.

The solid electrolytic capacitor 2 illustrated in FIG. 3(a) is producedby the above-described method.

Other Embodiments

The solid electrolytic capacitor according to the present invention isnot limited to the above-described embodiments. Variations andmodifications may be made to the structure, production conditions, etc.of the solid electrolytic capacitor within the scope of the presentinvention.

In particular, the method for electrically connecting the core part tothe anodic outer electrode is not limited to the methods described inthe first and second embodiments. Although the core part 11 b (the anodepart 22) is electrically drawn to the surface of the sealing resin 20through the first and second anodic via electrodes 41 and 42 in thesolid electrolytic capacitor 1 illustrated in FIG. 1(a) and the corepart 11 b (the anode part 22) is electrically drawn to the surface ofthe sealing resin 20 through the first anodic via electrode 41 in thesolid electrolytic capacitor 2 illustrated in FIG. 3(a), the solidelectrolytic capacitor according to the present invention does notnecessarily include the anodic via electrode, such as the first anodicvia electrode. Alternatively, for example, a lead frame may be disposedon the bottom surface of the capacitor element 10 or 10′. In the casewhere the anodic via electrode is not formed, the sealing resin is notnecessarily disposed on a portion of the core part in which the cathodepart is not formed.

In the solid electrolytic capacitor according to the present invention,the number of the anode terminals is not limited to one; the solidelectrolytic capacitor may include two or more anode terminals asdescribed in the first embodiment. Similarly to anode terminals, thenumber of the cathode terminals is not limited to one; the solidelectrolytic capacitor may include two or more cathode terminals.

REFERENCE SIGNS LIST

-   -   1, 2 SOLID ELECTROLYTIC CAPACITOR    -   10, 10′ CAPACITOR ELEMENT    -   11 VALVE-ACTING METAL SUBSTRATE    -   11′ RECESS    -   11 a POROUS PART    -   11 b CORE PART    -   12 DIELECTRIC LAYER    -   13 SOLID ELECTROLYTE LAYER    -   14 CONDUCTIVE LAYER    -   15 INSULATING LAYER    -   20 SEALING RESIN    -   21 CATHODE PART    -   22 ANODE PART    -   30 CATHODIC OUTER ELECTRODE    -   31 CATHODIC VIA ELECTRODE    -   31′ BUMP ELECTRODE    -   40 ANODIC OUTER ELECTRODE    -   41 FIRST ANODIC VIA ELECTRODE    -   42 SECOND ANODIC VIA ELECTRODE    -   45 VIA HOLE

The invention claimed is:
 1. A solid electrolytic capacitor, comprising:a valve-acting metal substrate including a core part having an uppersurface and a porous part disposed on a central portion of the uppersurface of the core part such that a lateral end of the upper surface ofthe core part is not covered by the porous part and an outer edge of theporous part extend above the upper surface of the core part; adielectric layer formed on an upper surface of the porous part; a solidelectrolyte layer disposed on an upper surface of the dielectric layer;a conductive layer disposed on an upper surface of the solid electrolytelayer; an electrically insulating layer formed on the upper surface ofthe lateral end of the core part and covering the outer edge of theporous part; a sealing resin located on the conductive layer and anupper surface of the insulating layer; a cathodic outer electrodelocated on the sealing resin and being electrically connected to theconductive layer by a cathodic via electrode which extends through thesealing resin; and an anodic outer electrode electrically connected tothe core part.
 2. The solid electrolytic capacitor according to claim 1,wherein the cathodic via electrode is a paste electrode including amaterial formed by curing a conductive paste.
 3. The solid electrolyticcapacitor according to claim 1, wherein the cathodic via electrode is acolumnar metal pin.
 4. The solid electrolytic capacitor according toclaim 1, wherein, the upper surface of the core part is a planar surfaceand the cathodic outer electrode has a larger size than the cathodic viaelectrode when viewed in a direction normal to the plane of theprincipal surface of the capacitor element, so as to cover the cathodicvia electrode.
 5. The solid electrolytic capacitor according to claim 1,wherein the insulating layer is composed of the same material as thesealing resin.
 6. The solid electrolytic capacitor according to claim 1,wherein the anodic outer electrode and the cathodic outer electrode aremetal electrodes including a metal film.
 7. The solid electrolyticcapacitor according to claim 1, wherein the anodic outer electrode andthe cathodic outer electrode are paste electrodes including a materialformed by curing a conductive paste.
 8. The solid electrolytic capacitoraccording to claim 1, wherein the anodic outer electrode is a ball-liketerminal.
 9. The solid electrolytic capacitor according to claim 1,wherein the cathodic outer electrode is a ball-like terminal.
 10. Thesolid electrolytic capacitor according to claim 1, wherein a stressrelaxation layer is interposed between the conductive layer and thesealing resin.
 11. The solid electrolytic capacitor according to claim1, wherein a damp-proof membrane is interposed between the conductivelayer and the sealing resin.
 12. The solid electrolytic capacitor ofclaim 1, wherein the porous part of the valve-acting metal substrate asa periphery and the lateral end of the core part extends around theentire periphery the porous part.
 13. The solid electrolytic capacitorof claim 1, wherein an anodic outer electrode is connected to the corepart by a anodic via electrode which extends through a portion of theinsulating layer which is located above the upper surface of the lateralend of the core part.
 14. The solid electrolyte capacitor of claim 13,wherein the anodic via electrode penetrates the sealing resin at alocation over the insulating layer.
 15. The solid electrolyte capacitorof claim 14, wherein the anodic via electrode comprises a first anodicvia electrode which penetrates the sealing resin and a second anodic viaelectrode which penetrates the insulating layer at a location disposedon the core part.
 16. The solid electrolytic capacitor according toclaim 15, wherein each of the first and second anodic via electrodes hasa tapered cross-sectional shape wherein the width of the taperedcross-sectional shape increases in the direction from the core parttoward the anodic outer electrode.
 17. The solid electrolytic capacitoraccording to claim 15, wherein the first and second anodic viaelectrodes are columnar metal pins.
 18. The solid electrolyte capacitorof claim 1, wherein the cathodic outer electrode located on the sealingresin and is electrically connected to the conductive layer by aplurality of cathodic via electrodes, each of which extends through thesealing resin.
 19. A solid electrolyte capacitor, comprising: (a) avalve-acting metal substrate including: (i) a core part having an uppersurface and a recess extending from the upper surface to a positionbelow the upper surface, the recess having a bottom and side walls; and(ii) a porous part disposed on the bottom and side walls of the recess;(b) a dielectric layer formed on an upper surface of a portion of theporous part located on the bottom of the recess and being spaced fromthe side walls of the recess; (c) a solid electrolyte layer disposed onan upper surface of the dielectric layer and being spaced from the sidewalls of the recess; (d) a conductive layer disposed on an upper surfaceof the solid electrolyte layer and being spaced from the side walls ofthe recess; (e) an electrically insulating layer located between theporous part on the one hand and the dielectric layer, the solidelectrolyte layer and the conductive layer on the other; (f) a sealingresin located on the conductive layer and an upper surface of theinsulating layer; (g) a cathodic outer electrode located on the sealingresin and being electrically connected to the conductive layer by acathodic via electrode which extends through the sealing resin; and (h)an anodic outer electrode electrically connected to the core part. 20.The solid electrolyte capacitor of claim 19, wherein: the sealing layeris located on the upper surface of the core part; and the anodic outerelectrode is located on the sealing layer at a position above the uppersurface of the core part; and an anodic via electrode which extendsthrough the sealing layer to electrically couple the anodic outerelectrode to the core part.
 21. The solid electrolyte capacitor of claim20, wherein the cathodic outer electrode located on the sealing resinand is electrically connected to the conductive layer by a plurality ofcathodic via electrodes, each of which extends through the sealingresin.
 22. The solid electrolyte capacitor of claim 19, wherein therecess has a parallelepiped shape.
 23. The solid electrolyte capacitorof claim 19, wherein the recess has a rectangular parallelepiped shape.